The present invention relates to long term information storage and retrieval in both human and machine readable format on optical media.
A traditional method of archiving human readable information is to record documents on microfilm. These documents may originally be in the form of paper, photographic film and the like, as well as electronic data generated by computer. The microfilm recording process involves exposing photosensitive film to demagnified images of the documents. After the film has been exposed, it is subjected to wet chemical processing to develop the images. The recorded documents are usually read by projecting their magnified images on to a screen, or by enlarging them with a television camera and a video monitor. With typical de-magnifications of up to 25xc3x97, the storage density of microfilm is on the order of 50 Mbits/inch2. When properly stored, the microfilm is estimated to have a life of up to 500 years.
A limitation of microfilm is that the film must be chemically processed prior to the retrieval of the stored information. As such, documents are usually recorded onto microfilm in groups. Once a piece of microfilm has been developed no further documents can be recorded on that particular film. The chemical development process itself leaves waste silver and other chemicals which need to be disposed. Another limitation is that microfilm has little gray scale capability and no color capability, thus its use is limited to high contrast, black and white text documents and drawings. Finally, few systems are available to mechanically interface the microfilm to automated libraries, or the recorded information to computer systems.
With the advancement of computer storage technology, information is increasingly stored in digital form. Documents not already in digital form are converted into Tagged Image File Format (TIFF) or similar electronic file formats using a document scanner, and stored on magnetic tape, optical disks, or the like. For retrieval or viewing, the documents are reconstructed from the electronic files and displayed on monitors or printed onto paper. Storage densities for the magnetic tapes and optical disks typically exceed 100 Mbits/inch2. The magnetic tapes can be compatible with conventional tape library systems when mounted in standardized cartridges that allow for automated handling. Likewise, optical disk handling can be automated. Data on the magnetic tapes have a stored lifetime of 10 to 20 years. Optical disk data lifetimes are estimated to be around 30 to 60 years. Both magnetic tape and optical disks, however, are vulnerable to the rapid advancements in computer storage technologies that make their readers obsolete. In order to have the information in readable form 100 years from now the information on existing magnetic tape and optical disks will have to be migrated periodically to new media to maintain compatibility with the changing read/write equipment.
The Kodak Archive Writer has improved on the storage capacity over microfilm by using rolls of 16 millimeter film and increasing the de-magnification to 40xc3x97. Each document is input as a TIFF electronic file which is used to modulate the intensity of a spot formed on a cathode ray tube (CRT). The CRT spot is optically imaged on to the film, which is exposed with a visual image of the document by appropriately scanning the CRT spot. As with the microfilm, prior to document retrieval the entire roll is subjected to wet chemical processing to develop the images. Retrieval of the information is accomplished with a television camera and computer which recreates the TIFF files from the visual images.
Another approach for long term storage is the Rosetta System proposed by Norsam Technologies. In the Rosetta System visual information is written into a silicon wafer using electron beam exposure or ion implantation. This requires the use of an energetic scanning electron beam or ion beam in a vacuum chamber. The silicon is then depth-etched using an etch-stop technique to form a master disk. This wet chemical processing results in similar batch limitations as microfilm. Documents are stored at 850xc3x97 de-magnification at a density of over 2 Gbits/inch2. Reading of the visual images is accomplished with a high-powered microscope equipped with phase contrast or interference-optics.
Consequently, a need has developed for a document storage approach which will allow the documents to be retrieved decades into the future without the need for readers which have long since become obsolete. The approach must accommodate documents of various sizes, resolutions, those containing shades of gray and color, and it must allow for new documents to be added to or retrieved from the storage media at any time. For ease of integration with existing computer systems the document storage approach should be compatible with current automated removable-media library systems and allow for storage in digital formats.
The object of the present invention is to provide a system and a method for storing documents for long periods of time. In particular, the invention starts with the documents in an electronic file format and ends with the documents stored in de-magnified human readable format on an optical recording medium so that the documents can be retrieved using a microscope. A Table of Contents and file headers containing indices and other metadata regarding each document may be included to help identify, locate and manage the documents during read-out. The optical recording medium is direct laser writeable to allow additional documents to be added and retrieved at any time.
A further object of the invention is that the information contained in the electronic files is processed prior to writing to accommodate shades of gray, color, and different resolutions of the documents.
Yet another object is that the documents can be stored in both digitally encoded and human readable form on the same physical media.
In carrying out these objects, the above objects, and other objects, features and advantages of the present invention will be readily apparent upon consideration of the following detailed description of the best mode for carrying out the invention in conjunction with the accompanying drawings.